(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Circuits"

Introduction to Electronics: Resistance Is Futile 



Make] Projects 

hhiiilH ho/ 1 !/ tuMaal/ chare r\icf*f\\tat* 



build, hack, tweak, share, discover,- 



Introduction to Electronics 



Resistance Is Futile 



Written By: KRA5H 



Step 1 — Introduction to Electronics: The 555 Timer Integrated Circuit (IC) 

• The 555 Timer IC was introduced 
by a company called Signetics 
(later bought out by Philips) in 1972 
and was designed by Hans R. 
Camenzind in 1971. 

• The 555 chip has 25 transistors, 15 
resistors and 2 diodes in an 8 pin 
DIP (Dual In-line Package) and 
looks like a square bug with eight 
legs. 

• It has a notch at the top and Pin 1 
is in the top left corner. 

• Picture source 




© Make Projects 



www.makeprojects.com 



Page 1 of 1 1 



Introduction to Electronics: Resistance Is Futile 



Step 2 



* 








(® 


© ©' 




* o 


2 


l /~\ a 






• 
©3 


■ 


7© 




* •/ 


1 


C SOCKET 




J 


4 


5 6 




I® 


® ©, 





• Insert the 555 timer chip into the 
Snap Circuits Eight-Pin IC Socket 
block (?U8). Make sure that the 
notch in the top of the 555 timer 
chip is aligned with the diagram of 
the chip pictured on the IC socket 
block. 



© Make Projects 



www.makeprojects.com 



Page 2 of 1 1 



Introduction to Electronics: 


Resistance Is Futile 




Step 3 



© Make Projects www.makeprojects.com Page 3 of 1 1 



Introduction to Electronics: Resistance Is Futile 



Ground 




Vcc 



Discharge 



Threshold 

Control 
Voltage 



• Pin 1 is ground. It is connected to 
the negative side of your battery or 
power supply along with any other 
components in your circuit 
connected to ground. 

• Pin 2 is the Trigger pin. It will be 
connected to ground and thus 
switches on pins 3 and 7. 

• Pin 3 is the Output pin. In this 
circuit it outputs a square wave 
signal that can be heard on a 
speaker. 

• Pin 4 is the Reset pin. It is not 
used in this circuit. 

• Pin 5 is the Control pin. It is not 
used in this circuit. 

• Pin 6 is the Threshold pin. The 
capacitor that we will connect to 
the 555 will charge up and when it 
reaches about 2/3 Vcc (voltage 
from the battery), this is detected 
by the Threshold pin. This will end 
the timing interval and send Ov to 
the Output pin 3 (switch it off). 

• Pin 7 is the Discharge pin. It is also 
switched off by the Threshold pin 6. 
When switched off, it cuts the 
power to the capacitor causing it to 
discharge. Pin 7 also controls 
timing and is connected to the 50K 
ohm Variable Resistor RV. Moving 
the slider on RV changes the 
resistance thus changing the timing 
and the pitch heard on the speaker. 

• Pin 8 is connected to the positive 



© Make Projects 



www.makeprojects.com 



Page 4 of 1 1 



Introduction to Electronics: Resistance Is Futile 



side of your battery or power along 
with any other components in your 
circuit connected to positive. 



Step 4 




Add the Snap Circuits blocks to the 
base grid as demonstrated in the 
picture. 



Step 5 




• Add the Snap Circuits blocks to the 
base grid as demonstrated in the 
picture. 



© Make Projects 



www.makeprojects.com 



Page 5 of 1 1 



Introduction to Electronics: 


Resistance Is Futile 




Step 6 



© Make Projects www.makeprojects.com Page 6 of 1 1 



Introduction to Electronics: Resistance Is Futile 




• Once you complete the circuit, 
switch on the 9 Volt Battery Holder 
(B5). You will hear a tone from the 
Whistle Chip. Move the slider on 
the Variable Resistor (RV) and you 
will hear the tone rise and lower in 
pitch depending on which way you 
move the slider. 

• The 555 chip is in "astable mode" 
which means that Pin 3 is sending 
a continuous stream of pulses 
called a square wave signal to the 
piezoelectric speaker (WC) that 
you hear as a tone. The square 
wave signal is caused by the 
charging and discharging of the 
capacitor. When you switch on the 
power: 

• Step 1 . The capacitor charges 
up. When the charge in the 
capacitor reaches 2/3 Voltage, 
this is detected by pin 6, the 
Threshold pin. 

• Step 2. The Threshold pin 6 
switches off the Output pin 3 and 
pin 7, the Discharge pin. 

• Step 3. When the Discharge pin 
7 is switched off this cuts the 
power to the capacitor which 
causes it to discharge. When the 
discharging capacitor reaches 
1/3 Vcc, this is detected by the 
Trigger pin 2. 

• Step 4. The Trigger pin 2 sends 
voltage from the battery to pin 3 



© Make Projects 



www.makeprojects.com 



Page 7 of 1 1 



Introduction to Electronics: Resistance Is Futile 



(the Output pin) and same 
voltage to pin 7 (the Discharge 
pin) which causes the capacitor 
to charge up (go back to step 1). 

• This process repeats creating the 
square wave signal and you hear 
that signal from the speaker as a 
tone. 

• When you move the slider on the 
Variable Resistor (RV) this 
changes the resistance of the 
circuit. Since the Variable resistor 
is connected to pin 7, changing the 
resistance controls the timing of 
how often the capacitor charges 
and discharges which changes the 
pitch you hear from the speaker. 



Step 7 



BATTERY 
SWAP 



H 5V 


5V 




'© © 


& 




- 






0><S 


wy*o 





9V Holder & SW: 

5V - regulated 5V outputs 
(-) - power return to battery 
Snap for 9V battery 
ON/OFFswftch 



• To power the 555, you can use the 
Snap Circuits B5 block (it is also 
called a 9 volt Holder and Switch). 
The advantage to using this block 
is that you can connect a standard 
9 volt battery to the block and it will 
deliver a reliable 5 volts to the 555 
through the L7805 voltage regulator 
circuit (see circuit schematic). 

• The B5 also has two 5 volt outputs- 
-one to power the 555 circuit and 
one that you can use to power 
another device. 



© Make Projects 



www.makeprojects.com 



Page 8 of 1 1 



Introduction to Electronics: Resistance Is Futile 



Step 8 — Introduction to Electronics: Resistance Is Futile 




•MS ?«S 



• If you will recall from my guide Introduction to Electronics: The Diode , you had to add a 
100-ohm resistor into the circuit. Its purpose was to limit the current flowing through the 
LED to protect it. 

• If you put too much current through an LED, it will burn out. With a POP! And sometimes 
pieces of plastic will fly off. And it will stink. Then you'll have to buy a new LED. 

• Consider the water pipe analogy: when water flows through a pipe, the pipe offers very 
little resistance to the flow of water. If, however, a bunch of rocks are inserted into the 
pipe, this will increase the resistance against the flow of water through the pipe. 

• As electrons flow through a wire or conductor, there is very little resistance to the electron 
flow. 

• If you were to connect an LED directly to a battery without a current limiting resistor too 
much current will flow throught the LED and POP! 

• Another way to think of it is filling a water balloon with a garden hose. If you put a kink in 
the hose this will limit the flow of water making it easy to fill the water balloon, but if you let 
go of the kink in the hose, the water balloon will fill too quickly and burst. 



© Make Projects 



www.makeprojects.com 



Page 9 of 1 1 



Introduction to Electronics: Resistance Is Futile 



Step 9 




• To get an idea of how resistance can affect a circuit, let's try a couple of experiments with 
the 555 tone generator circuit. 

• In this first video , I replace the two-snap conductor-which has very little resistance-with 
the [a] 100-ohm resistor, [b] 1K-ohm resistor, [c] 5.1K-ohm resistor, [d] 10K-ohm resistor, 
and finally [e] 100K-ohm resistor. Listen to the change in sound as I replace each resistor. 

• In this next video I used the 555 tone generator to create a pencil lead organ. I drew a 
thick bar on a piece of paper with a Number 2 pencil and I taped the white jumper wire to 
one end. Listen to the change in sound as the electrodes move across the pencil mark. 

• If we compare the two videos it might be easier to figure out what is happening in the 
circuit. When the blue jumper wire is closest to the white jumper wire, the pitch is highest 
and when it is farthest away from the white jumper wire the pitch is lowest. 

• In the first video when I replaced the two-snap conductor with the 100-ohm resistor, the 
pitch changed only very slightly. When I inserted the 1K-ohm resistor, the pitch got lower. 
With the 5.1K-ohm resistor the pitch got lower still and so on until the 100K-ohm which 
caused the pitch to be the lowest. 

• We can then deduce that as resistance increases in the circuit, the pitch gets lower. 
Conversely, as resistance decreases, the pitch gets higher. Recall that we are changing 
the resistance on the circuit connected to pin 7 of the 555, which controls the timing of how 
quickly or how slowly the capacitor charges and discharges. 

• As resistance increases the capacitor charges and discharges more slowly and the pitch 
gets lower. As resistance decreases the capacitor charges and discharges more quickly 
and the pitch gets higher. 

• You may thus find this circuit useful for testing the relative resistance of different 
substances. Obviously it won't be as useful as a multimeter, but you have built a simple 
audio resistance tester. 



© Make Projects 



www.makeprojects.com 



Page 10 of 11 



Introduction to Electronics: Resistance Is Futile 

This document was last generated on 201 2-1 1 -1 8 09:32:57 AM. 



© Make Projects www.makeprojects.com Page 11 of 1 1